Patented Jan. 5, 1954 2,665,317

UNITED STATES PATENT OFFICE 2,665,317. METHOD OF TREATING RUBBER OBTAINED FROM RUBBER-BEARING PLANTS Frederick E. Clark and Irvin C. Feustel, Salinas, Calif., assignors to the United States of America as represented by the Secretary of Agriculture. No Drawing. Application November 14, 1951, Serial No. 256,356 4. Claims. (CI. 260-818) (Granted under Title 35, U. S. Code (1952), sec. 266). 1. 2 A non-exclusive, irrevocable, royalty-free The resulting product is the crude resinous license in the invention herein described, for all guayule rubber of commerce. It contains an governmental purposes, throughout the World, average of about 20-25%, resin (acetone or alco with the power to grant sublicenses, for Such pur. hol. Soluble constituents). This gross impurity poses, is hereby granted to the Government of limits the usefulness of guayule rubber and for the United States of America. this reason efforts are being made to develop a This invention relates to a method for treating deresination process by means of which a crude natural rubber extracted from various shrubs, rubber of superior quality can ultimately be pro wines, and other plants for the purpose of pre duced. venting clumping or cohesion of rubber particles 0. The Wet rubber worms, as recovered from the during handling and processing. The method scrub milling, operations are roughly comparable is specifically applicable to rubber obtained from in size to grains of rice and they possess a micro the guayule shrub (Parthenium. argentatun, Sponge-like structure. At this point in the proc Gray), one of the most promising sources of nati ess the Worms are regarded as being generally ural rubber that can be grown in the United best suited for deresination by solvent extraction states, in which connection it will be described because of their favorable size, granular condi in detail. tion, and pervious structure. Hence, efforts are In the recovery of rubber from guayule by the being, made to develop a deresination process conventional mechanical extraction process, the based on the use of wet scrub-milled worms. At harvested shrub is first defoliated, comminuted, 20 and crushed. This material is then milled in a times, however, the worms clump or cohere to water slurry with pebbles in a pebble. mill until form relatively, large and impervious aggregates the rubber is completely released from plant or maSses which cannot be eXtracted because the resin solvent will not penetrate the lumps that cells and agglomerated into macroscopic particles have been formed. Clumping may take place to or granules commonly called "worms.” The 25 varying degrees at any stage in the pebble mill pebble-milled slurry is then discharged into a ing process although operational difficulties due flotation tank wherein additional water is added to clumping. have principally been focused on the and the mixture thoroughly stirred to facilitate Scrub; milling step since this is the most critical separation of the worms from the plate-material one from the standpoint of applying corrective (bagasse). After standing for a short period, the 30 treatments for worms already clumped and for rubber worms, float to the surface of the Water attaining a Well dispersed or non-cohering con while the bagasse sinks. The Worms are recov dition in which the worms are suitable for drying ered by skimming the flotation tank. The Worms or for resin extraction. are then given a hydrostatic. pressure treatment It is frequently very difficult and at times im in hot water at 500 p.s. i. or greater, to water 3. possible, to break up all the clumps or to prevent log cork fragments which floated with the rub further clumping in the scrub mill. Sometimes ber in the first flotation. After this pressure the lumps or aggregates of worms become so treatment the worms are given a second flotation, large, as to weigh. Several pounds. Clumped similar to the first. The waterlogged cork frag rubber is not only impossible to deresinate effec ments now sink and the Worms are again. 40 tively; but is also unsuitable for drying because skimmed from the flotation tank. The Worms the normal-sized Worms in the mixture become are next subjected to a scrubmilling treatment, Over-dried and degraded by the prolonged heat This constitutes pebble milling of a slurry of the ingnecessary to dry, the lumps. worms in hot water, followed by a third flotation It is necessary to keep the Worms submerged for final purification from adhering or imbedded 45 in Water if there is a break in processing con plant fibers. The quantity of Water used for tinuity or a delay in transport from one proc scrub milling is usually about 20 parts to 1 of essing step to another in order to minimize rubber (dry basis). The ratio of Water to rubber clumping and also to protect the rubber from ex in the flotation tank is about 100 to 1. The Wors posure to air. Since it is very susceptible to oxida skimmed from the third flotation are usually 50 tion, unless an antioxidant has been applied. spread out on trays and dried in a vacuum drier. However, if worms are held in a container for 2,665,817 3. 4. more than a few hours a closely cohering maSS any of the materials known to have the ability of rubber is usually formed which requires con to disperse insoluble materials in aqueous media, siderable effort to break up into individual Worms. Thus for example One may use polyoxyethylene Steam treatment is often resorted to in such sorbitan monolaurate; polyoxyethylene lauryl cases but at best this has only a temporary bene alcohol; dialkyl esters of Sulphosuccinic acid ficial effect. such as dihexyl sodium Sulphosuccinate, dioctyl The rubber possesses some tackiness and con sodium sulphosuccinate; the sodium salt of de sequently there is a natural tendency for a mass hydrogenated roSin; Sulphated higher alcohols of worms to cohere especially under conditions such as sodium dodecyl sulphate, Sodium tetra where the pressure resulting from its own weight decyl sulphate, sodium hexadecyl Sulphate; al becomes appreciable and the period of contact kylated aromatic Sulphonates Such as Sodium is prolonged. decyl benzene sulphonate, sodium dodecyl ben In some cases a high degree of clumping is zene sulphonate, sodium tri(isobutyl) benzene caused by a rapid cooling of the water or other sulphonate, Sodium alkylated (C12 to C18) ben liquid in which the worms are being processed or 5 Zene Sulphonate, etc. The insoluble Soap in the colntained. In other cases clumping is associated dispersion may of course be derived from any of with certain physiological influences of the shrub the metals and fatty acids, or mixtures, referred from which the rubber is milled since the difficul to above. ties are more pronounced during the shrub Instead of applying the pre-formed insoluble flowering season. Also, rubber milled from young 20 Soap to the rubber particles, the in Soluble Soap shrub has a greater tendency to clump than rub may be formed in situ on the rubber particles or ber from old shrub. in the coating bath by interaction of (1) a The object of this invention is to treat the higher fatty acid or water-soluble salt thereof worms in such a manner as to prevent clumping With (2) a Salt of a metal Which forms Water or cohesion of the individual Worms. A further 25 insoluble soaps. Thus specific methods of form object is to provide a treatment which will re ing the insoluble Soap coating on the rubber par tain its effectvieness not only with regard to han ticles are as follows dling of the worms prior to deresination but also (a) Interaction of a higher fatty acid such as during deresination and/or in preparation of the stearic acid with a Water-Soluble Salt of a metal rubber for drying. 30 which forms water-insoluble soaps, as for ex We have found that the above objects can be ample, calcium chloride, zinc chloride, or other attained by coating the worms with a thin film Water-soluble SaltS of the metals previously re of a water-insoluble metallic Soap, that is, a ferred to. water-insoluble salt of a metal and a higher fatty (b) In the above technique (d), the fatty acid acid. The insoluble soap film prevents the Worms 35 may be replaced by a Water-soluble salt thereof from clumping during handling or processing of Such as an alkali metal salt. Thus one could use the worms as in the various milling, flotation, and for example Sodium stearate or an Ordinary soap hydrostatic pressure operations. Moreover, the Which consists of the sodium salts of a mixture of insoluble soap-coated worms will not clump even higher fatty acids. if held en masse for a prolonged period of time. (c) Interaction of a higher fatty acid such as Furthermore, the film does not prevent moisture stearic acid with the metallic ions such as cal vapor from passing off readily during drying nor cium and/or magnesium contained in hard water does it prevent penetration of a Solvent such as in which the rubber is processed. acetone during deresination. Still further, the (d) In the above technique (c), the fatty acid insoluble soap film does not have any adverse is replaced by a water-soluble fatty acid salt such effect on the quality of the rubber. as Sodium stearate or ordinary soap. The insoluble soap may be derived from many In applying the procedures outlined above the different materials. Thus, the metal moiety of rubber worms may be first contacted with a solu the insoluble soap may be any metal which forms tion or dispersion of the fatty acid (or water an insoluble soap, as for example, zinc, cadmium, Soluble Salt of a fatty acid) and then contacted aluminum, magnesium, lead, calcium, strontium, With a Solution of the insoluble soap-forming barium, tin, mercury, and so forth. Metals such metal Salt (or hard water). Obviously, if de as copper, manganese, and iron are operative sired, this sequence of operations can be reversed. but their use is not advised because these metals In these manners of operation it is evident that may catalyze oxidation of the rubber. the insoluble soap film will be formed in situ on The fatty acid moiety of the insoluble soap the Surface of the rubber worms. Another may be any of the higher fatty acids as for ex method of applying our technique is to add both ample, capric, lauric, myristic, palmitic, mar the fatty acid (or water soluble salt thereof) plus garic, stearic, arachidic, oleic, and so forth. Mix the insoluble Soap-forming metal salt to an aque tures of fatty acids derived from natural Sources 60 ous bath and then immerse the worms in this such as coconut oil, tallow, lard, soybean oil, pea bath. In Such type of operation the insoluble nut oil, cottonseed oil, and so forth are effective soap will be formed in the bath in minute par and economical. ticles which will be adsorbed on the porous sur The insoluble soap coating may be applied in face of the worms. It is obvious that if hard several different ways. Our preferred method is 65 Water is used, no metal salt need be added. To to directly apply the insoluble metallic Soap to assist in dispersing the minute particles of in the rubber worms. To this end, an insoluble Soap Soluble Soap throughout the coating bath, any of such as zinc stearate is made up into an acqueous the previously mentioned dispersing agents lay dispersion with the aid of a dispersing agent. be used. The Worms are then treated With this a queous 70 For convenience, the insoluble soap coating dispersion in such manner as to achieve good may be deposited on the rubber particles during contact between the entire Surface of the Worms One of the aqueous milling procedures in which and the dispersion, thus for example the Worms the Worms are formed or refined. Thus prefer may be agitated in a bath of the aqueous disper ably, the insoluble Soap film is deposited on the sion. As the dispersing agent we may employ 75 Worms in conjunction with the scrub milling op 2,665,317 5 6 eration. A typical procedure is to add stearic tendency to clump at any time: In comparision, acid (or Sodium stearate or ordinary Water-sole rubber. Worms which were treated in the Waring uble soap) to the Water to be used in the Scrub blendor in either distilled or hard tap water alone mill in an amount corresponding to about:1% of became badly clumped almost immediately after the dry. ... Weight of the rubber Worms to be 5 blendor treatment. This was observed also where processed. The water is heated with steam to either, the Stearic acid or the calcium chloride about 90° C. and the volume adjusted so that was omitted from the treatment. when the Worms are introduced the ratio of the weight of water to that of dry rubber will be Ea’ample 2 about 20:1, as normally used in scrub milling. 10 Fifty grams of wet, guayule rubber worms as re The charge of rubber worms, also previously covered from the Secondary flotation. Wei'e mixied heated with steam and stirred to disperse it as for 5 minutes in a Waring blendor with 350 ml. thoroughly as possible, is dumped into the scrub hard water at 90° C. containing 0.25 g. com mill containing the Stearic acid-hot water"mix mercial soap powder (Ivory Snow). The Worms ture and milling action Started. The mill is op after treatinent showed no evidence of clump erated for about thirty minutes, after which the ing after standing several days. charge is dumped into a flotation, tank and the WOrms recovered by skimming in the usual man Eacample 3 ner. In this illustration the water used was hard Fifty grams of wet guayule rubber worms as re Water, containing. Sufficient calcium and mag 20 covered from the secondary flotation were mixed nesium to react with the stearic acid to produce for 3 minutes in a Waring blendor with 475 ml, the desired insoluble soap film. It is evident that of hard water at 90° C. containing 0.125 g. stearic instead of hard water, one could use soft or dis acid. The worms showed no evidence of clump tilled water and dissolve in it the amount of a ing after standing several days. metal. Salt Such as Zinc chloride or calcium chlo 25 ride required to react With the stearic acid to Eacample. 4 form the insoluble Soap. As an alternative to Fifty pounds of wet rubber worms were scrub treatment of Worms in the scrub mill, the com milled in a pilot plant size batch pebble mill for minuted shrub may be treated as it enters the 30 minutes at 70° C., using hard water containing pebble milling circuit. By this means clumping 0.5 pound added Stearic acid. The Weight ratio of rubber can be prevented anywhere in the of water to dry weight of rubber was 20:1. After proceSS. discharging into a flotation tank and skimming, The insoluble soap is effective in the range of the Wors were allowed to stand in water in a 0.1 to 5% based on the estimated dry weight of large kettle for a day. The WOrms remained non rubber. We prefer to use approximately 0.5 to 3. 5 adhering and granular and showed no tendency 1% Soap (calculated as stearic acid) when treat Whatever to cohere Or clump. A control scrub ing rubber Worms in conjunction with scrub mill Iihilling conducted at the same time was badly ing Since We have found that quantities within clumped. Both the stearic acid treated rubber this range are adequate to give the desired re and the cointrol rubber Were deresinated With the Sults. However, it is necessary to use more soap use of Several changes of acetone in a large kettle (up to 10% based on the dry weight of the rub 4. fitted with an air-driven stirrer. No difficulty ber) when treating comminuted shrub in the WaS encountered in deresinating the worms hav pebble mill as when treating rubber worms in the ing the in Soluble Soap film whereas considerable Scrub mill. difficulty was found in stirring the control be The following examples demonstrate the in cause of clumping of the worms in the latter. Ap vention in greater detail. These examples are proximately 15% of the control batch had to be furnished only by Way of illustration and not discarded at the end of the extraction because of limitation. lumps which are incompletely extracted. The The hard water employed in Examples 2, 3, and Stearic acid treated batch yielded 29 pounds of 4 had the following composition: deresinated rubber having a residual resin con ) tent of 2.80% (hot ethanol extract) and a Mooney Content in viscosity of 91.5. The control after discarding Constituent parts per lumps yielded 25 pounds of deresinated rubber Inillion having a residual resin content of 1.92% and a Mooney viscosity of 93. The slight difference in calcium------magnesium------4.0716.0 55 residual resin (as measured analytically by hot chloride------51.5 ethanol extraction) and in Mooney viscosity be Sulphate------.88 tween the two batches does not indicate any known quality difference caused by the stearic Eacample 1 acid treatment. Fifty grams of wet guayule rubber Worms as 60 Eacample 5 recovered from the secondary flotation were A 250 g. Sample of comminuted guayule shrub placed in a Waring blender containing 475 ml. (moisture approx. 40%) which has been crushed distilled Water previously heated to 180° F. and twice through laboratory crushing rolls was placed containing 0.125 g. Stearic acid (present as a 65 in a laboratory “attritor.' The attritor is a type melted film on the Surface of the Water). This of pebble inill in which a vertical shaft with hori amount of Stearic acid is equivalent to approxi ZOntal members rotates through a mass of small mately 0.5% of the dry weight of the rubber. pebbles while the mill shell remains stationary. Sufficient calcium chloride (approx. 0.03 g.) to A dispersion of 2.2 g. of zinc stearate prepared react with all of the Stearic acid was added and 70 With the aid of 0.22 g. of dioctyl sodium sulpho the whole mixed by the blendor for 3 minutes. Succinate in 800 ml. of cold tap water was added The rubber was then removed from the blendor, to the comminuted shrub in the attritor. Small placed in a beaker with fresh water and allowed pebbles in the amount of 2700 g, were then placed to stand several days. The worms remained in in the apparatus and the mixture milled for 30 a Wholly non-adhering condition and exhibited no 75 minutes at a rotor speed of 300 R. P. M. The 2,665,817 7 8 slurry thus formed was subjected to a flotation resinate the worms, the improvement which com treatment using a water to rubber ratio of 100:1. prises coating the worms with a water-insoluble The worms were clean and fine in size and showed metallic soap prior to the extraction whereby to no tendency to cohere even when pressed together prevent agglomeration of the worms without in between the fingers. A control milling carried out 5 terference with the penetration of the solvent. with the same shrub in the same manner but 3. In the process wherein resinous guayule without the zinc Stearate produced worms which worms are subjected to solvent extraction to de were not as fine and which could not be sepa resinate the worms, the improvement which com rated after pressing between the fingers. The prises agitating the worms, prior to the extraction, Stearate treated worms were demonstrated to be 10 in an aqueous medium containing a dispersion of readily deresinated with acetone yielding a rub a water-insoluble metallic Soap whereby to coat ber of lighter color than the control. the worms with the water-insoluble metallic soap Having thus described our invention, we thus to prevent agglomeration of the worms with claim: out interference with the penetration of the sol 1. A process of preparing deresinated guayule 15 vent. rubber which comprises Subjecting guayule to 4. The process of claim 3 wherein the aqueous aqueous milling Operations to form and purify the medium additionally contains a dispersing agent. guayule rubber Worms, at least one of the milling operations being in the presence of a Water-in FREDERICK E. CLARK. Soluble metallic Soap to coat the worms with the 20 RVN. C. FEUSTE. Water-insoluble metallic Soap, and extracting the coated worms with an organic solvent to de References Cited in the file of this patent resinate the Worms, the Water-insoluble metallic soap-coating preventing agglomeration of the UNITED STATES PATENTS worms without interference with the penetration 25 Number Name Date of solvent. 2,019,055 Noble ------Oct. 29, 1935 2. In the process wherein resinous guayule 2,035,437 Stan ------Mar. 24, 1936 worms are Subjected to Solvent extraction to de 2,434,412 (Jones ------Jan. 13, 1948